This invention relates to an acceleration sensor, and particularly relates to a technology that enables the adjustment of the sensitivity of the acceleration sensor (made by microfabrication) to be easily performed, and enables the determination whether the acceleration sensor is defective or non-defective to be easily performed.
Generally, a three-dimensional acceleration sensor includes a supporting part for fixing the acceleration sensor to an external board or the like, a weight part, and a deformable beam part that connects the supporting part and the weight part. The conventional three-dimensional acceleration sensor is composed of a laminated structural body. One type of the laminated structural body is made by laminating a plurality of layers on which the supporting part, the weight part and the beam part or the like are formed. The other type of the laminated structural body is made by microfabrication to form the weight part or the like on a laminated board such as SOI (Silicon On Insulator) having been previously laminated.
The present invention relates to the three-dimensional acceleration sensor made by microfabrication on the laminated board.
The three-dimensional acceleration sensor is manufactured by the following process. First, a laminated board including three layers is prepared. The three layers are referred to as first, second and third layers in order beginning at the uppermost layer. Piezoresistive elements are formed on portions of the first layer of the laminated board corresponding to the beam parts. The patterning is performed on the first layer (i.e., the top side of the laminated board), and then the patterning is performed on the third layer (i.e., the bottom side of the laminated board). The acceleration sensor manufactured by such a process is disclosed in, for example, Japanese Laid-Open Patent Publication No. 2004-198243. The publication also discloses the structure and the manufacturing process of an acceleration sensor having a stopper for enhancing the impact resistance and a reinforcing member provided on the stopper.
However, in order to adjust the sensitivity of the conventional acceleration sensor, it is necessary to change the length of the beam part by changing the positions of the supporting part and the weight part. Thus, it is necessary to change the positions of the through holes formed on the top side and the bottom side of the laminated board, and therefore it is necessary to change the layouts on the top side and the bottom side of the laminated board. Accordingly, it is not easy to adjust the sensitivity of the acceleration sensor.
Moreover, in the conventional acceleration sensor, it is difficult to align the through holes formed on the top side and the bottom side of the laminated board with each other. Therefore, it is necessary to pick up several acceleration sensors as samples and to destruct each sample to thereby observe the cross section of each sample using SEM, TEM or the like. Therefore, it is difficult to align the through holes formed on the top side and the bottom side of the acceleration sensor, without destructing the acceleration sensor.